This invention relates to wheelchairs, and in particular to a wheelchair which is structured to negotiate curbs and other obstructions with a minimum of effort expended by the wheelchair occupant. In particular, the invention pertains to a wheelchair where the center of gravity of the wheelchair need not be raised or lowered to surmount an obstacle.
The greatest barrier facing any occupant of a wheelchair is an obstruction, normally street curbs and the like. While recent programs of forming curb cuts in curbs have greatly facilitated the mobility of wheelchair occupants, given the sheer numbers of street curbs and other similar obstructions, it is doubtful that they all will ever be reconstructed to accommodate wheelchair occupants.
In the past, various efforts have been made to adapt wheelchairs to surmount curbs and other obstacles. For example, U.S. Pat. No. 4,455,029 discloses a structure with outboard auxiliary wheels which are raised or lowered to raise or lower the wheelchair to surmount a curb. U.S. Pat. No. 3,905,437 is similar, having outboard rear wheels and a central jack which are used to raise or lower the wheelchair. Other examples of wheelchairs having various devices and structures to raise and lower the wheelchair are found in U.S. Pats. No. 4,747,611; 3,573,877; 4,132,423; 2,701,005 and 4,618,155.
All of the above efforts to provide obstacle negotiating wheelchairs suffer a common disability of their own. Each requires the center of gravity of the wheelchair to be raised or lowered. Because the occupant is in the wheelchair at the time, the occupant must work against his or her own weight, if the wheelchair is mechanically operated, and if it is electrically or otherwise operated, a complex mechanism must be employed of sufficient strength to handle the weight of the occupant of the chair. Thus, considerable energy must be expended, and when the occupant is called upon to expend such energy, often he is unable to do so, whether it is by sheer lack of strength or due to injury or disability. Thus, such obstacle negotiating wheelchairs have found little utility.